docs: def Stichlmair_dry(Vg, rhog, mug, voidage, specific_area, C1, C2, C3, H=1.):
      r'''Calculates dry pressure drop across a packed column, using the
      Stichlmair [1]_ correlation. Uses three regressed constants for each
      type of packing, and voidage and specific area.
  
      Pressure drop is given by:
  
      .. math::
          \Delta P_{dry} = \frac{3}{4} f_0 \frac{1-\epsilon}{\epsilon^{4.65}}
          \rho_G \frac{H}{d_p}V_g^2
  
      .. math::
          f_0 = \frac{C_1}{Re_g} + \frac{C_2}{Re_g^{0.5}} + C_3
  
      .. math::
          d_p = \frac{6(1-\epsilon)}{a}
  
      Parameters
      ----------
      Vg : float
          Superficial velocity of gas, Q/A [m/s]
      rhog : float
          Density of gas [kg/m^3]
      mug : float
          Viscosity of gas [Pa*s]
      voidage : float
          Voidage of bed of packing material []
      specific_area : float
          Specific area of the packing material [m^2/m^3]
      C1 : float
          Packing-specific constant []
      C2 : float
          Packing-specific constant []
      C3 : float
          Packing-specific constant []
      H : float, optional
          Height of packing [m]
  
      Returns
      -------
      dP_dry : float
          Pressure drop across dry packing [Pa]
  
      Notes
      -----
      This model is used by most process simulation tools. If H is not provided,
      it defaults to 1. If Z is not provided, it defaults to 1.
  
      Examples
      --------
      >>> Stichlmair_dry(Vg=0.4, rhog=5., mug=5E-5, voidage=0.68,
      ... specific_area=260., C1=32., C2=7, C3=1)
      236.80904286559885
  
      References
      ----------
      .. [1] Stichlmair, J., J. L. Bravo, and J. R. Fair. "General Model for
         Prediction of Pressure Drop and Capacity of Countercurrent Gas/liquid
         Packed Columns." Gas Separation & Purification 3, no. 1 (March 1989):
         19-28. doi:10.1016/0950-4214(89)80016-7.
      '''
      dp = 6*(1-voidage)/specific_area
      Re = Vg*rhog*dp/mug
      f0 = C1/Re + C2/Re**0.5 + C3
      return 3/4.*f0*(1-voidage)/voidage**4.65*rhog*H/dp*Vg**2